ADDITIONAL FUNDING is being sought to avoid a six-month hiatus in flight testing of the Boeing/Sikorsky RAH-66 Comanche scout/attack helicopter. The first prototype is due to be grounded from April to September 1998, because of a lack of cash.
The US Army is seeking an extra $40 million in 1998 funding to avoid the grounding, having secured additional money to prevent a similar flight-test interruption this year.
Boeing/Sikorsky has completed some 35h testing of the Comanche prototype since the first flight took place in January 1996. The aircraft has been flown to 145kt (270km/h) and 1.75g. "We're about 70% through initial envelope-expansion," says flight-test director Clarence Hutchinson.
The team had planned to have completed envelope expansion, but a transmission failure on the propulsion-system testbed resulted in the aircraft being limited to 84% power, preventing the prototype from reaching its design horizontal speed of 170kt.
Hutchinson says that the resonance which caused the input bevel-gear to fail has been overcome by attaching an elastomeric damper to the gear web. The aircraft is cleared to be flown for 45h with the original transmission, and is scheduled to be grounded in April for installation of the redesigned gearbox.
Flight testing is planned to resume on 30 June, and will go "full bore" for the rest of the year, according to Hutchinson. Goals for 1997 include demonstrating the 170kt forward speed, 45kt sideward and rearward flight and 90í snap turns at 80kt.
The remaining 10h before gearbox removal are being spent flight testing fairings on the torque tubes, which transmit pitch-change commands to the main-rotor blades. This is expected to reduce loads on the horizontal stabiliser and is one of several solutions planned to overcome tail problems. Increased stabiliser incidence has successfully reduced tail loads; Hutchinson says that small "Gurney" flaps attached to the stabiliser trailing-edge have eliminated roll caused by asymmetric loads. Structural changes to the vertical stabiliser have overcome vibration problems, he says.
Boeing/Sikorsky is working under a $1.7 billion "Phase III" contract awarded in January for Comanche demonstration/validation. This runs until October 2001 and includes flight testing of two prototypes and construction of six more early-operational-capability RAH-66s for evaluation by the US Army. Initial operational capability is planned for December 2006, with six aircraft.
While Comanche funding remains uncertain, the first McDonnell Douglas Helicopter Systems AH-64D Apache Longbow attack helicopter for the US Army was rolled out at the company's Mesa site in Arizona on 21 March, following the maiden flight, which took place four days earlier.
The helicopter is the first of 232 AH-64As to be remanufactured as "D" Apache Longbows under a five-year $1.9 billion contract. The US Army aims eventually to have its fleet of around 750 AH-64s remanufactured into Ds, of which 227 will carry the Northrop Grumman mast-mounted Longbow millimetre-wave radar. The balance will be compatible with the radar-carrying models and will be upgraded with the same advanced avionics, more powerful General Electric T700-701C turboshafts and Lockheed Martin Hellfire missiles equipped with RF seekers.
The first remanufactured AH-64D is a veteran of Operations Desert Shield and Desert Storm during the 1991 Gulf conflict.
Source: Flight International
